Venture capitalists John Doerr and Ted Schlein of Kleiner Perkins Caufield
& Byers have had a front-row seat at Silicon Valley's recent Web froth and
its fallout.

Their venture firm in the past decade made a big bet on clean technology. In
the last couple of years, Kleiner has also put money into high-profile and
fast-growing digital startups, but only after they were valued at $1 billion or
more—a far cry from the firm's traditional strategy of investing very early in
young companies.

Some of those more recent investments—in companies such as messaging service
Twitter Inc., mobile-payments service Square Inc. ...